The German patent publication 29,909,529 U1 discloses various forms of such a controller device, several valve modules being collected together in each case to constitute an array-like unit and such unit being either designed to be self-supporting or being placed on a plate-like module carrier. The valve modules each comprise a principal valve serving for the control of a principal valve subject to positive or negative pressure medium pressure and at least one electrically operated valve drive serving for the operation of the principal valve.
If the controller devices are employed in complex machines there is a need for a precise monitoring of the operational state of the principal valves. Such monitoring has so far been performed visually using optical inspection means, which indicate the switching state of the valve drive. It would also be feasible to detect the switching state of the valve drives electrically, for example on the basis of amperage measurement. In all cases there is however the disadvantage that from the switching state of the valve drive no conclusions may be drawn about the operational state of the principal valve. Owing to trouble conditions for example the switching over of the principal valve may be prevented, although the valve drive has been activated.